1. Field of the Invention
The present invention relates to means for controlling the variable setting of the flow straightener vanes for the compressors of turbine plants, especially aircraft turbojet engines, in the case of variably settable flow-straighteners with a substantial displacement or adjustment range.
2. Summary of the Prior Art
There are in existence two types of control rings for variably settable flow-straighteners:
(a) control rings which are integral with the compressor casing and move circumferentially on bearings machined on the outside of the casing; and
(b) control rings which are external to the compressor casing and move both circumferentially and linearly in an upstream or downstream direction following the angular movement of the control links connected to the vanes of the flow-straightener, the only points of contact between the ring and the outside of the casing being, for example, shoes intended to maintain the ring concentrically with respect to the casing.
We are concerned with this second type of control ring. In engines in which the variably settable vanes require only a small angular adjustment (as in the state of the art shown in FIG. 1), the control links are mounted so that shafts of the links rotate in radial guide bushes on the ring and are subjected to a twisting .beta. proportional to the set angle of the vanes. If the displacement is very small, as shown in FIG. 1, this twisting of the links is acceptable.
If the displacement is more substantial, U.S. Pat. No. 4,050,844 proposes inserting between the shaft of each link and the radial bush of the ring a barrel-shaped spring or an elastomeric buffer of the same shape in order to withstand the torque. However, these intermediate members are crimped on the shaft of the link and when they wear or break, it is the entire link that has to be changed.
On the other hand, when the angle of adjustment of the vanes is substantial and the diameter of the compressor is small, which is more and more frequently the case in supersonic engines with high compression ratios and small overall size, the above-mentioned arrangements are no longer usable as the torques that have to be borne by the intermediate members are too great.
French Patent No. 1 190 067 suggests placing on the shaft of each link a ball joint to replace the torsional strain by a rotation of the ball joint on outer rings with spherical bearings. In addition to their wear problems, these universal ball joints require the provision of a great number of parts and are often heavy and cumbersome.
It is an object of the present invention, therefore, to provide means for controlling the setting of flow-straightener vanes having a large angle of adjustment which is simpler and lighter than ball joint mechanisms and which, nevertheless, imposes no torsional stress on the control links.